How to treat post herpetic neuralgia?

Treatment of Post-Herpetic Neuralgia

Start with gabapentin as first-line therapy, initiating at 300 mg on day 1,600 mg on day 2, and 900 mg on day 3, then titrating to 1800-3600 mg/day in three divided doses, as recommended by the American College of Physicians and FDA labeling. 1, 2

First-Line Treatment Options

Gabapentin (Preferred Initial Agent)

• Gabapentin is the recommended first-line oral pharmacological treatment with proven efficacy across 1800-3600 mg/day, though no additional benefit is demonstrated above 1800 mg/day 1, 2
• The FDA-approved titration schedule is: 300 mg on day 1,600 mg/day (divided twice daily) on day 2, and 900 mg/day (divided three times daily) on day 3, with subsequent titration to 1800 mg/day (600 mg three times daily) 2
• Maximum dosing interval should not exceed 12 hours between doses due to saturable absorption kinetics 3
• An adequate trial requires 3-8 weeks for titration plus 2 weeks at maximum tolerated dose 3
• In elderly patients or those with renal impairment, start with 100-200 mg/day and titrate more slowly 4, 3
• Dose adjustment is mandatory in renal dysfunction: for CrCl <15 mL/min use 100-300 mg/day as single daily dose; for CrCl ≥60 mL/min use 900-3600 mg/day in three divided doses 3, 2

Topical Lidocaine 5% Patches

• Topical lidocaine patches provide excellent efficacy (NNT = 2) with minimal systemic absorption, making them ideal for elderly patients or those with comorbidities 1
• Can be worn for 12-24 hours on affected areas, particularly suitable for localized pain 1
• This is the safest option due to negligible systemic effects 4

Tricyclic Antidepressants

• Nortriptyline is preferred over amitriptyline with excellent efficacy (NNT = 2.64) and better tolerability 1, 5
• Start at 10-25 mg at bedtime and increase every 3-7 days to a final dose of 25-100 mg at bedtime 1
• Timing at bedtime minimizes daytime sedation effects 1

High-Concentration Capsaicin

• The 8% capsaicin dermal patch provides pain relief for at least 12 weeks 1
• Apply 4% lidocaine for 60 minutes before capsaicin application to mitigate erythema and pain side effects 1

Second-Line Treatment Options

Pregabalin

• Consider pregabalin if gabapentin provides inadequate response, with NNT of 4.93 1
• Effective dose typically ranges from 150-600 mg/day in two divided doses 4, 1
• May be preferred over gabapentin for initial trial due to pharmacokinetics supporting easier and more rapid titration 4
• Start with 25-50 mg/day in elderly patients, with lowest doses for moderate or greater renal impairment 4

Opioids (Use with Caution)

• Opioids (oxycodone, extended-release morphine, methadone) show efficacy (NNT = 2.67) but should not be used as first-line agents due to risks of pronociception, cognitive impairment, respiratory depression, endocrine/immunological changes, and potential for misuse and addiction 1
• Tramadol shows efficacy with NNT of 4.76 and may be considered as a safer opioid alternative 1

Combination Therapy

• Combining morphine with gabapentin may be more effective when single agents provide inadequate relief, allowing lower doses of each medication while providing additive effects 1

Treatment Algorithm

1. Start with gabapentin using FDA-approved titration schedule (300 mg day 1 → 600 mg day 2 → 900 mg day 3 → titrate to 1800-3600 mg/day) 2

   • Alternative: Start with topical lidocaine 5% patches if pain is localized or patient is elderly with multiple comorbidities 1

2. If gabapentin is ineffective or not tolerated after adequate trial (3-8 weeks titration + 2 weeks at maximum dose), switch to nortriptyline 10-25 mg at bedtime, titrating to 25-100 mg 1, 3

3. If monotherapy fails, add topical lidocaine patches or consider combination therapy (e.g., gabapentin + low-dose opioid) 1

4. If still inadequate, trial pregabalin 150-600 mg/day in two divided doses 1

5. For refractory cases, consider high-concentration capsaicin 8% patch or interventional treatments 1, 6

Special Considerations and Common Pitfalls

Elderly Patients

• Always start with lower doses and titrate more slowly in elderly patients 4
• Topical treatments are particularly valuable due to minimal systemic effects 4, 1
• Gabapentinoids commonly cause somnolence, dizziness, and mental clouding in older patients, requiring careful monitoring 4

Medications to Avoid

• Lamotrigine is not recommended for PHN due to lack of convincing evidence of efficacy and risk of lamotrigine-associated rash 1

Duration of Treatment

• PHN may persist for months to years, and some patients require long-term treatment with no maximum duration specified 1
• Periodic reassessment is recommended as PHN may improve over time 1

Side Effect Management

• Approximately 80% of patients report somnolence with gabapentin, which is dose-dependent and can be minimized by starting low and titrating slowly 3
• Other common side effects include dizziness, dry mouth, and constipation 3

Non-Pharmacological Adjuncts

• Cognitive behavioral therapy, hypnosis, and physical/occupational therapy may provide additional benefit as part of multimodal therapy 1